(i) Field of the Invention
The present invention relates to an image pickup apparatus for picking up a subject image, particularly to an image pickup apparatus suitable for optically analyzing a test object.
(ii) Description of the Related Art
In a conventional art, an image pickup apparatus for picking up the two-dimensional image of a test object has heretofore been used, for example, in astronomical observation, analysis of materials constituting an object, analysis of a wavelength of a laser beam emitted from a semiconductor laser, observation of the combustion state of a fuel in the cylinder of an internal combustion engine, analysis of plasma, and other optical analyses of the states of various test objects.
However, as such image pickup apparatus, there has been only a general camera in which a photosensitive film is disposed in an image forming position (surface) by a lens for forming a subject image and the two-dimensional image of a test object is formed on the film, or a so-called digital camera in which an image sensor consisting of CCD or the like is disposed on the image forming surface of the lens and an electric signal obtained for each pixel constituting the image sensor is processed to generate the image data of a subject. Therefore, there is a problem that the image pickup apparatus suitable for optically analyzing the test object has not existed.
That is to say, in order to optically analyze various test objects as described above, it is necessary to photograph the test object with an invisible ultraviolet ray, an infrared ray or another specific-wavelength light. However, when this is realized by the conventional image pickup apparatus, it is necessary to prepare several types of filters which transmit only the light components having specific wavelengths, select a desired filter from the filters, and dispose the filter in front of the lens during photographing of the test object.
Therefore, in the conventional art, when the test object is photographed and optically analyzed, the filter attached to the image pickup apparatus has to be frequently changed, and much trouble is disadvantageously required for a photographing operation.
Moreover, when the image sensor consisting of CCD or the like is used to photograph the test object, the obtained image data can be processed using information processors such as a computer. An analyzing operation can efficiently be performed as compared with when the general camera is utilized. In the conventional image sensor, however, the dynamic range of the sensitivity of an image pickup elements such as CCD constituting each pixel of the image sensor is small, and further the sensitivity cannot be adjusted for each pixel (i.e., for each image pickup element).
Therefore, when the digital camera consisting of the image sensor is used as the image pickup apparatus for photographing the test object, the sensitivity of the entire image sensor needs to be adjusted in order to prevent the brightest portion of the image from causing a halation. However, with such sensitivity adjustment, when the subject image having a large brightness/darkness difference is photographed, the obtained image becomes so dark that the analysis operation of the test object is sometimes hindered.
An object of the present invention is to provide an image pickup apparatus which can easily obtain a high-precision two-dimensional image necessary for optically analyzing a subject as a test object.
To attain this and other objects, according to a first aspect of the present invention, there is provided an image pickup apparatus which includes a lens for forming a subject image in a predetermined position and in which the tip end surface of an optical fiber is disposed on a surface for forming the subject image by the lens via a support member. As a result, a light constituting the specific portion of the subject image formed by the lens is incident upon the optical fiber.
Moreover, the support member can be moved along the surface on which the subject image is to be formed via a driver driven and controlled in a predetermined scanning pattern by a scanner. When the driver is driven/controlled in this manner, the position of the support member, and the incident position of the light upon the optical fiber supported by the support member are gradually changed on the subject image forming surface.
On the other hand, a photodetector for converting the light transmitted via the tip end of the optical fiber into an electric signal is disposed on the terminal end of the optical fiber. The electric signal is inputted into an image data generator from the photodetector. Subsequently, the image data generator successively takes the electric signal from the photodetector in synchronization with the change of the light incident position upon the optical fiber on the subject image forming surface by the operation of the scanner. The signal level of the electric signal is associated with the incident position of the light upon the optical fiber, and stored in a storage medium.
Therefore, when the scanner moves and scans the light incident position upon the optical fiber along the subject image forming surface, the pixel data corresponding to the light brightness of each portion of the subject image formed by the lens is successively stored into the storage medium. Finally, the pixel data for one frame of the subject image is stored as the image data in the storage medium.
Therefore, when the image data stored in the storage medium is used to display the subject image on a display formed of CRT, liquid crystal display or the like, or when the image data is outputted to various printers such as an ink jet printer and a laser printer, and the subject image is printed on a desired sheet, a user can confirm the subject image from the displayed image or the printed image. Moreover, when information processors such as a computer are used to process the image data, a subject, that is, a test object can remarkably easily be analyzed optically.
Furthermore, in the present invention, when the subject image data is generated as described above, the tip end of the optical fiber is moved along the subject image forming surface, the light signal transmitted via the optical fiber is converted to digital data in each position of the moving optical fiber tip end, and the pixel data for one pixel constituting the image data is obtained. Therefore, as compared with the conventional image pickup apparatus for using the image sensor of CCD or the like to generate the image data, high-precision image data can remarkably easily be obtained.
That is to say, according to the image pickup apparatus of the present invention, while the tip end of the optical fiber is moved and scanned along the subject image forming surface, the photodetector is used to successively generate the pixel data constituting the subject image data on the terminal end of the optical fiber. Therefore, the resolution of the obtained image data corresponds to one control amount, that is, the change amount of the position of the light incident upon the optical fiber during driving/controlling of the driver by the scanner.
Therefore, when the scanner is adjusted so as to reduce this displacement amount, the resolution of the obtained image data can be enhanced. Conversely, when the scanner is adjusted so as to increase the displacement amount, the resolution of the obtained image data can be lowered. That is to say, the image pickup elements of CCD or the like is disposed on a plane in the image sensor for use in the conventional digital image pickup apparatus with which the image data can directly be inputted to the computer. Therefore, the resolution of the obtained image data is limited by the number of image pickup elements and an interval between the image pickup elements. According to the image pickup apparatus of the present invention, however, the resolution of the obtained image data can arbitrarily be adjusted.
Therefore, according to the image pickup apparatus of the present invention, it is possible to photograph even a fine test object, such as the section of the laser beam emitted from the semiconductor laser, which has been difficult to photograph with the conventional image sensor. Therefore, the application range of the image pickup apparatus can be enlarged.
Additionally, in order to enhance the resolution of the obtained image data in this manner, the driver needs to move the support member with a higher precision. For this purpose, according to a second aspect of the present invention, the driver is constituted of a pair of step motors for moving the support member in two axial directions which cross at right angles to each other. The position of the light incident upon the optical fiber may be changed by driving the respective step motors in a predetermined scanning pattern by the scanner.
That is to say, when the pair of step motors are used to move the support member in two axial directions (e.g., horizontal and vertical directions), the moving amount of the support member in each direction can be controlled in accordance with the number of driving steps of the step motor with a high precision. Therefore, according to a second aspect of the image pickup apparatus, the high-precision and high-resolution image data can easily be obtained.
Moreover, as described above, for the conventional image sensor, the dynamic range of the sensitivity of the image pickup elements constituting the image sensor is small, and the sensitivity needs to be adjusted in the entire image sensor. Therefore, when the subject with only the specific portion thereof being bright is photographed, the entire image becomes dark. In the image pickup apparatus of the present invention, however, since all the pixels constituting the image are extracted by one photodetector, the dynamic range of the sensitivity can arbitrarily be set. For example, when using a photoelectrically converting device having a large dynamic sensitivity range (e.g., a photomultiplier) as the detector, the image data in which the subject image is faithfully reproduced can be obtained.
Furthermore, in the image pickup apparatus of the present invention, since the image data is prepared by changing the position of the light incident upon the optical fiber and successively extracting the electric signal from the photodetector, a photographing time per one frame of the image is lengthened. However, by using the photodetector of which sensitivity is adjustable, the sensitivity of the photodetector can be adjusted in accordance with the level of the electric signal extracted from the photodetector during the preparation of the image data. In this case, even when the dynamic range of the sensitivity of the photodetector is relatively small, a clear image can be obtained by adjusting the level of the detection signal extracted by the image data generator to be optimum.
On the other hand, as described above, in order to optically analyze various test objects, it is necessary to photograph the test object with a specific-wavelength light including an ultraviolet or infrared ray. However, according to the image pickup apparatus of the present invention, when the test object is analyzed, it is unnecessary to perform the conventional operation for preparing several types of filters in advance, selecting the filter from the filters and disposing the selected filter before the lens. Additionally, the analyzing operation can also be performed remarkably easily.
That is to say, according to a third aspect of the present invention, in order to photograph a subject with the light having a desired wavelength by the image pickup apparatus of the present invention, there is provided a spectral unit for splitting the light transmitted via the optical fiber and passing only the light with a specific wavelength. The specific-wavelength light split by the spectral unit is inputted to the photodetector. Alternatively, according to a fourth aspect of the present invention, there is provided a distributor for distributing the light transmitted via the optical fiber into a plurality of paths, and a plurality of photodetectors capable of detecting the lights different in wavelength from one another are disposed on the respective paths of the lights distributed by the distributor.
According to the third aspect of the image pickup apparatus, the image data of the subject photographed with the desired light can be obtained. Additionally, when the spectral unit simply changes the wavelength of the light to be passed through the photodetector, a plurality of types of image data of the subject photographed with different wavelength lights can easily be obtained. Moreover, according to the fourth aspect of the image pickup apparatus, similarly as the third aspect, a plurality of types of image data of the subject photographed with the different wavelength lights can easily be obtained. Therefore, the image pickup apparatus of the present invention is remarkably suitable for optically analyzing the test object.